The present invention relates generally to a data embedding apparatus for embedding arbitrary information into data, an apparatus for extracting embedded data, and methods therefor, and a computer readable recording medium recording the methods, and more particularly to electronic watermark techniques for embedding information into an image.
In an electronic watermark technique applied to image data, a luminance value of pixels, a frequency component of an image, or the like is changed in such a portion in which even if data is changed, the change is not visually perceptible. Information is embedded by representing a bit value “0” or “1” or the like in the form of change in luminance value or frequency component.
Since an image embedded with information must not present any visual change therein, when compared with its original image, the conventional electronic watermark technique has the following two requirements:                1) An image into which a watermark is embedded is a digital content of a relatively large size which is composed of rather complicated shapes (or patterns) in a large number of colors, as represented by photographs, pictures and so on; and        2) A small amount of information is embedded. Conditions required to the electronic watermark techniques are described, for example, in Kobayashi et al., “Data Hiding Using the Nature of Neighboring Pixels—Statistical Nature of Neighboring Pixels”, Transactions of 56th National Meeting of Institute of Information Processing, pp. 3-37 to 3-38, 1998.        